Project Summary Temporomandibular joint disorders (TMJDs) are of unknown etiology and affect as many as 10 million Americans, with women 3-8 times more likely to be treated than men. The temporomandibular lateral capsule- ligament (LCL) complex spans the temporal bone and mandibular condyle, and through a pathologic `loose ligament' phenomena could lead to TMJD development by an inability to maintain physiologic approximation between articular components. Sexual dimorphisms in human LCL complex mechano-electro-chemical properties including incremental tensile stiffness and viscoelasticity, collagen ultrastructure, extracellular matrix fixed charge density and glycosaminoglycan composition could predispose females to TMJD development. In light of our recent reports on the sexual dimorphisms in the human temporomandibular disc, it is plausible to hypothesize sexual dimorphisms in mechano-electro-chemical properties also exist for the human LCL complex. The central hypothesis of this study proposal is that sex-specific differences exist in baseline human LCL complex incremental tensile stiffness and viscoelasticity, collagen fiber ultrastructure, extracellular matrix fixed charge density and glycosaminoglycan composition. Soft tissue tensile stiffness is commonly associated with collagen alignment and bundle size, while relative compositions of charged glycosaminoglycans (measured by fixed charge density) regulate tissue hydration and likely influence viscoelasticity. The proposed study seeks to define baseline human LCL complex incremental tensile stiffness and viscoelasticity, collagen ultrastructure, extracellular matrix fixed charge density and glycosaminoglycan composition, and investigate sexual dimorphisms potentially related to the increased prevalence of TMJDs among women. Aim 1 will determine baseline incremental tensile stiffness and viscoelasticity, and collagen ultrastructure of male and female human LCL complexes. An incremental stress-relaxation protocol will be used to define LCL complex tensile stiffness and viscoelasticity, and second-harmonic generation microscopy will define collagen ultrastructure in fresh, intact and unstained specimens to (1) determine sex-specific differences, and (2) assess LCL complex load-bearing function. Aim 2 will determine baseline extracellular matrix fixed charge density and glycosaminoglycan composition of male and female human LCL complexes. Fixed charge density, a regulator of tissue osmotic, and ionic/nutrient environment, is sensitive to sex specific differences in temporomandibular tissues and combined with glycosaminoglycan composition will (1) determine sex-specific differences, and (2) establish critical electrochemical and compositional properties relevant to tissue viscoelasticity and tissue osmotic and ionic/nutrient environment. Study results will advance our understanding of the human LCL complex and its plausible role in the increased prevalence of TMJDs among women, and could establish a precedent for studying sexual dimorphisms of temporomandibular tissues.